The Influence Of Defect States On The Damping Properties Of Lightweight Concrete

The vibration problem caused by public transportation is becoming more and more serious.The widely used vibration damping measures have not achieved good barrier effect.Therefore,it is significant to develop a new type of vibration damping material.As a kind of vibration-absorbing material,lightweight concrete has not yet formed a complete theoretical system of vibration reduction design.The theory of phononic crystals in solid physics was proposed in the 1990 s.The phononic crystal is a kind of periodic composite material with the property of suppressing the propagation of elastic waves.The elastic band gap characteristics of phononic crystals are used to provide vibration damping and isolation.Based on the two-dimensional three-component local resonance model,this paper explores the band gap characteristics of the periodic structure of lightweight concrete,and studies the influence mechanism and variation law of defect state on its damping characteristics,and realizes the defect state to light.The band gap distribution and attenuation effect of lightweight concrete are optimized,and the influence of the periodic detuning on the damping characteristics of the lightweight concrete is also discussed.The main research contents of this paper are as follows:Based on the two-dimensional three-component local resonance model of lightweight concrete,the plane wave expansion method combining super-cells is derived,and the calculation of the energy band structure under the defect state is realized.The transmission characteristic calculation model was established by using finite element software to evaluate the attenuation effect of the finite periodic structure.The defect state is introduced by changing the vibrator spacing and changing the resonance characteristics.By analyzing the vibration mode and energy distribution of the band gap opening,the influence mechanism of the two introduction methods on the damping characteristics of lightweight concrete is explored.The vibrator spacing can improve the localized effect of the elastic wave,and the wide band gap is achived.The defective unit after changing the resonant characteristic can form a new local resonant structure to open a new band gap at a specific frequency.Introducing the defect state in the periodic structure of lightweight concreted by introducing the defect unit,the hole and the gap,and the variation of the band gap distribution and attenuation effect with the defect parameters is explored.The damping characteristics of lightweight concrete is Optimized.The results show that the introduced defect unit acts as a new local resonance structure,and the elastic wave vibration is localized in the defect unit,then,a new band gap is opened.The introduction of holes in different regions of lightweight concrete can improve the localized effect of the elastic wave of the resonance unit,and changing the resonance characteristics of the defective unit can generate a new local resonance type band gap,thereby extending the wide band gap distribution range.Introducing a certain number of slits can change the composition of the local resonance structure and realize the band gap moving to the low frequency.The periodic detuning model of lightweight concrete was established.The effects of random layer detuning on the vibration damping characteristics of lightweight concrete were studied.The results show that the increase of the degree of detuning makes the band gap open position move to the low frequency.At the same time,the low-frequency attenuation effect of the lightweight concrete is enhanced.In addition,the band gap range attenuation effect can be optimized by the artificially designed uniform detuning structure.